MARINE CITY, Mich. — Some Michigan law enforcement agencies are stepping up security efforts following online threats against schools.

The Marine City Police Department says it's investigating after a Twitter post was spotted that targeted the principal at the Marine City Middle School. Police say the East China School District is taking precautionary measures this week to ensure safety.

There have been a number of threats in Michigan since a massacre that killed 17 high school students and faculty last week in Florida.

Berrien County authorities and the FBI are investigating a threat reportedly made about St. Joseph High School. School officials say worries may have been stoked by miscommunication based on overheard conversations and posts on social media.

Authorities also investigated a potential threat related to South Lyon High School in suburban Detroit.